Electric furnace



C. H. VOM BAUR.

ELECTRIC FURNACE.

APPLICATION man 0ec.3o, 191a.

1,385,41 1 Patented July 26, 1921.

E- c lwvenfoq,

cam. nA svom VBAUR, or DOUGLASTON, NEW YORK.

ELECTRIC FURNACE,

v I Specification of Letters Patent.

Patented July 26', 1921.

Application filed December so, 1918. Serial No. 268,910.

To all whom it may concern:

Be it known that I, CARL HANS VoM BAUR, a citizen of the United States, and a resident of Douglaston, in the county of Queens and State of New York, have invented certain new and useful Improve ments in Electric Furnaces, of which the following is a specification.

My present 1I1V6I1t1011 relates to electric furnaces, and particularly those embodying three electrodes, and has for its object to insure a uniform or approximately unlform distribution of the current, or rather of the heat produced thereby, particularly in cases where a three phase distribution of current is employed- In order to. obtain this result, Ihave devised a novel shape ofthe furnace,

and a'novel arrangement of the electrodes within such furnace,,as willnow be explained in detail, and partlcularly pointed out in the appended claims.

Reference'is tobe had to the accompanyin drawings, in which:

Figure l is a vertical section onthe plane indicated by the line 11 of Fig. 2, representing a satisfactory and preferred embodiment of my invention;

Fig. 2 is a horizontal section, substantiall on the line 2-2 of Fig. 1;

Fig.3 is a partial vertical-'sectlon on line 3-3 ofFig. 2 and v Fig. 4 is a diagram illustrating certain relations in the contour shape of the fur-f nace, as set forth hereinafter.

At T, I have indicated atransformer by. which a polyphase current supplied through the wires .10, 11, 10 (say from an ordinary alternator, not shown) is converted into suitable three-phase current, to be "led through the three wires 12, 13 14: to the electrodes 15,

16, and 17 respectively of the electric furnace. Of course, if a threebase current of suitable(generaly low) .vo tage is avail able, directly, the transformer T will not be required. .The electrodes pass, through the top or roof 18 of the electric-furnace, madeof any suitable refractory material. The said electrodes are preferably employed in a vertical position, as shown, and are also preferably adjustable up and down, for

which purpose they may pass or slide through suitable holders, indicated at 19.

The furnace, which .in 'plan view is of a .i generally elliptical shape at least at the slag line (plane of section 2 -2), is provided with a discharge spout: 2,0, primarily for the pouring ofthe metal or other material amounts of heat.

normal working position.

under treatment, which preferably forms part of the electric circuit. This spout may be located at any suitable point, say at one of the ends of the furnace. i

and is provided with one or more doors 22, one directly behind the spout 20, and'the other, say diametrically opposite. By opening these doors, access. is had to the inter1or of the furnace forthe purpose of inspection, patching, charging, rabbling off sla etc.

with the three-phase, three-wire arrange ment, described, each of the three electrodes w1ll receive the same amount of current, and they will therefore develop like The aim of my invention 1s to ,lIIS UIB that, under these. conditions, ever 1 point of the sidewall of the body 21 at the contour of the slag line, will receive approximately the same total or aggregate amount of .heat from the three electrodes,

when the mass within the furnace is molten;

To meet this requirement accurately, the

outline or contour, at the slag line should be formed, theoretically, according to a curve p The furnace bottom or body 21 is preferably cup-shaped of constantly changlngradius of curvature similar to an ellipse; for practical purposes, however, 1t w1ll:'be sufficient to have this contour composed of two circular arcs at the middle of the furnace, having their common center at thepoint or lower end of the central electrode 16, and two circular arcs at the ends of the furnace, the centers of these end arcs being in linewith and equidistant from, the center of the middle arcs. The centers of the end arcs are at the points or lower ends of the lateral elec trodes l5, 17 when the latter are in their The operative ends of the three electrodes. are therefore normally in line with each other (either exmay or approximately) along what may be termed the major axis of the furnace, with the two lateral electrodes at equal distances from the central electrode. The radius of the middle arcs is greater than that of the end arcs, and there'is a definite novel relation, to be explained presently,between the major and the minor axes of the contour and the distance separating the lateralelectrodes from the central electrode. preferred example illustrated by- Figs. 1, 2 and 3, the lateral electrodes 15, 17 are just half-way between the central electrode and the ends of the major axis, and in this par- In the 1' I ticular case, taking the distance from the 1' central electrode to one of the lateral electrodes as the unit, 1, the radius of the middle arcs would have to be approximately 1.28 (the radius of each end are in this case being 1). In the construction shown adjacent arcs are connected by straight lines tangent thereto.

To develop and explain the general relations between the several dimensions of the furnace, or rather of its contour, reference will be made to the diagram Fig. 4, where C desi nates the location of the central electrodefD and E the location of the lateral electrodes, F the generally elliptical contour of the furnace (at the slag line), viewed in plan, A a point of said contour in line with D C E, and B a point of said contour on a line (minor axis) drawn through the center 0 perpendicular to the major axis A D O E. Let a designate the major radius (A C), Z) the minor radius (B C), e the eccentricity (C D or C E) of the points D and E, and (Z the distance from the point B to either of the points D and E.

Inasmuch as each electrode produces an equal amount of heat, and inasmuch as the heat at any point is in inverse ratio to multiplying by 6 we obtain and further the square of its distance from the source of heat, the heat at the point A will be 1 1 l (ae) (a+e) and the heat at the point B will be 1 2 b b +e Since it is desired to have an equal amount of heat at the points A and B, we have the and s i-x For the purpose of simplifying the calculation of numerical examples, we may designate the fraction equation (7 to the more convenient form In the specific construction illustrated by Figs. 1 2 and 3, the distance between the of the side wall t two lateral electrodes is'equal to the diame-. ter of the circles of which the end arcs form p=ig=.7347

and

Of-course, when (2:1, as assumed in connection with Fig. 2, and m=2, 00 becomes equal to b, and the minor radius or half ing value of b determined therefromwith the aid of the equation or formula given,

. In the operation of my improved furnace," I prefer to extend the vertically-adjustable electrodes to the mass of materialund'er treatment, and to have the conducting molten bath of metal or other material form. I

therefore,-will be substantially uniform at part of the circuit between the electrodes.

With the, new arrangement described, I

am enabled, when operatin with a threephase current and three-conductors or wires,

leading to the electrodes, to obtain a practically uniform heating of the side wall of the furnace throughout its contour, and I thus avoid temperature strains which might cause deformation or other injury to said furnace wall. ,In furnaces of this general type employing, at the electrodes, a current of more than two phases, a uniform heating roughou-t its contour has not been obtained hitherto, and this resulted in objectionable features. It will be obvious that the relatively hot portions of an unevenly heated side wall will burn out more quickl than others, and on'the other hand, the re atively cooler portions are likely to cause trouble on account of an uneven melting action. If the furnace is used, say for meltin a cold charge of metal, this material will melt less at the relatively cooler portions of the side wall, and in order to mitigate this defect and to hasten the melting, it has been the practice heretofore to open the furnace doors and to push the unmelted metal from such cold spots into the hotter portions of the furnace. All of this is unnecessary when my improved arrangement is adopted, which msures a distribution of the electric current and a heating effect 1 (temperature gradient) which are practically uniform throughout the marginal pormeans, such as tion of the furnace, Much greater durabilityiand jefiiciency are thus secured by my improved -furnace, the oval or elliptical form, of which is also of advantage in giving the molten bath a relatively large surface area.

1; This'is of special value when treating metals,

sincethe thoroughnessof the refining action 7 depends largely on the quantity of slag in contact with the metal to be treated, and this quantity is increased, relatively, when using an oval form of furnace as described.

In the particular form illustrated, my invention is applied to an electric furnace of' the arc type, the three electrodes of which are connected to Wiressupplied with threephase currents, and specifically. to the con ductors of thelow-tension side of a transformeror alternator. However, I do not.

limit myself to the so-called fdelta7 connection shown in Figq. l, but may use equivalent t e star or Y connection. Thesemodifications and others may be made without departing from the nature of my invention as defined in the appended claims. It willbe understood that in a furnace constructed in accordance with the principle of the presentrinvention uniform temperature'of the-furnace walls and consequently uniform action of the slag on the walls will bemaintained. .The corrosion of the walls,

different points along the walls. This is due to: the fact that the aggregate heating effect of the electrodes, with uniform energy in each arc, is practicallythesame at different" points along the walls, for example, at the ends of the major and minor axes. The statement that the heat is practically the same as used here and in the claims is intended to define the condition in the furnace which has been constructedsubstantially in accordance with the principle of the invention, as defined in the specification.

Even without extraneous means for the automatic regulation of the electric heat, a furnace of the construction set forth, will lnsure a practically uniform application and distribut on of heat, the thermal efficiency of the furnace being also increased since the heat gradient is practically the same in all parts of the furnace.

I claim:

.1. An electric furnace whose contour in plan view, is of generally elliptical shape with three electrodes adapted to be supplied with three-phase current and placed one at the center of said furnace, and the others at equal distances therefrom on the major axis of said furnace at such points as to satisfy the equation where a indicates one-half of the major axis on which the electrodes are situated, Z2 one-half of the minor axis, and e the distance from the central electrode to each of the lateral electrodes.

2. An electric furnace whose outline, in plan View, comprises two end portions curved according to arcs of circles of equal radii but different centers, and two middle portions curved according to arcs of a circle whose center is in line with, and equidistant from, the centers of the end arcs; the radius Z) of the middle arcs, the distance 6 between the center of the middle arcs and the centers of the end arcs, and the distance a from the center of the middle arcs to those points of the end arcs which are in line with the centers of all the arcs, being so proportioned as to satisfy the equation 3. An electric furnace whose contour, in plan View, comprises two end portions curved according to arcs of circles of equal radii but different centers, the distance between said centers being equal to the diameter of said circles, and two middle portions curved according to arcs of a circle the center of which is halfway between the other two centers, and the radius of which is about 1.28 times the radius of one of the end arcs.

4. An electric furnace whose contour, in plan View, is of generally elliptical shape, with three electrodes adapted to be supplied with three-phase currents and placed one at the center of the furnace and the others on the major axis of said figure, halfway between the center and the ends of such axis,

the minor axis being equal to about .ea times the major axis.

5. An electric furnace whose contour, in plan View, is of generally elliptical shape, with three electrodes located within the furnace, anda three-phase, three-wire circuit connected with said electrodes, the latter plurality of electrodes so located within said contour that at the slag line at the periphery the aggregate heating effect of all the electrodes with uniform energy in each arc is practically the same at the ends of the major axis of said figure as at the ends of its minor axis.

7 An electric furnace whose contour, in plan View, is a curvilinear figure, with a plurality of electrodes so located within said contour that at the slag line at the periphery the aggregate heating effect of all the electrodes with uniform energy in each arc is practically the same for all points of said curvilinear contour figure.

CARL HANS VOM BAUR. 

